Step 1

Put 2 or 3 small saucers in the freezer; they'll be used to quickly cool teaspoons of jam to find when the setting point has been reached.

Step 2

Put 4 washed, rinsed and drained jars and lids on a baking tray and place in the oven at its lowest setting.Turn off the oven when the jars are hot, but leave them inside until you're ready to pot the finished jam.

Step 3

Peel the marrow or courgette.Cut it open, remove the seeds and discard them.Chop the flesh into small pieces and put into a large, wide pan.

Step 4

Peel and core the apples, chop finely and put in the pan with the marrow or courgette.

Step 5

Remove the peel from one of the lemons, leaving behind as much of the bitter pith as you can.Put the peel in a piece of muslin cloth along with the bruised ginger, tie it up (use string if necessary) and add it to the pan.

Step 6

Stir in the water then switch on the heat. Gently cook until both the marrow or courgette and the apple are very soft (approx 30 min). Stir occasionally to prevent sticking or burning.

Step 7

Take off the heat, push the muslin bundle to one side and mash the contents of the pan with a potato masher.

Step 8

Add the juice of both lemons and tip in the sugar.Stir until the sugar dissolves, then put the pan back on the heat.

Step 9

Turn up the heat and bring the contents to a boil – you can put a lid on for this stage to speed it up.

Step 10

As soon as the jam has come to the boil, take the lid off and keep at a rolling boil until setting point is reached (15 - 30 min).To test for setting point:Take the saucepan off the heat.Flake test: Take some jam on a wooden spoon, cool it a little, then let it fall off the edge of the spoon. If the final bits of jam come together into 'flakes' rather than running off in a stream then proceed to the Saucer test. If it doesn't flake, boil for another 4-5min then test again.Saucer test: Take one of the cold saucers from the freezer, put a teaspoon of jam on it to cool then gently push the jam with your finger. If it wrinkles then setting point has been reached. If not, boil for another 4-5 min then test again.

Step 11

Once setting point has been reached, remove the muslin bundle, take your jars from the oven and pack the jam into them. Protecting your hands, put the lids on and leave to cool.

Step 12

When the jars are cold, tighten the lids a little more if possible. Label and store in a cool, dark place.Ready to use immediately but unopened jars should keep at least a year.